Fabry-Perot interferometers are used as optical filters and in spectroscopic sensors, for example. A Fabry-Perot interferometer is based on two mirrors, whereby a Fabry-Perot cavity is formed into a gap between the mirrors. The pass band wavelength of a Fabry-Perot interferometer can be controlled by adjusting the distance between the mirrors i.e. the width of the gap. It is common to use micromechanical technology for producing Fabry-Perot interferometers. Such a solution is described e.g. in patent document FI95838.
A micromechanical interferometer usually includes a substrate and layers of two materials with different refractive coefficients, such as silicon dioxide and silicon. Mirrors of the interferometer are comprised of alternating layers of the two materials. A movable mirror is provided by removing a sacrificial layer, which has initially been formed between two mirrors. The position of a moveable a mirror is controlled by applying voltage to electrodes, which are included in the mirror structures.
The micromechanical production technology allows series production of interferometers. However, there are some disadvantages related with the prior art interferometer components. Prior art Fabry-Perot interferometers have high requirements for the packaging of the interferometer in order not to cause instability of the interferometer due to changing conditions. However, in many applications, such as automotive industry, the cost of the components must be kept low, and providing special packaging would cause the production cost to rise. It is also quite difficult to avoid changes of temperature of the environment from affecting the temperature of the interferometer. As a result, temperature drift occurs in the wavelength response of the interferometer, and the stability of the interferometer is not sufficiently high.